Variable grip blind rivet

ABSTRACT

A variable grip blind rivet has a rivet body with a first shank adapted to be inserted into a hole in a workpiece and having an axial bore, and a flange at a first end of the first shank for abutting the workpiece when the first shank is inserted into the hole in the workpiece. A mandrel has a head, for engaging a second end of the first shank, and a second shank adapted to extend through the axial bore. The head has an abutment portion for abutting the first end of the first shank. At least one protrusion adjacent the abutment portion defines a recess for receiving the first end of the first shank during setting of the rivet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. application Ser. No.12/850,114, filed Aug. 4, 2010, PCT Application No. PCT/GB2008/050824,filed Jan. 7, 2009, Great Britain Application No. 0801996.0, Filed Feb.4, 2008 and Great Britain Application No. 0803118.9, Filed Feb. 21,2008. The disclosure of the above-referenced application is incorporatedherein by reference.

The present invention relates to blind rivets.

Blind rivets are used in a variety of applications, from securing thinsheets to relatively thick components, and in a variety of materials,ranging from steel to plastics. The blind rivet enables lower costassembly to be achieved, but also contributes to the strength andintegrity of the resulting joint or fixing. For example, if a pair ofworkpiece sheets to be joined are slightly bowed, the rivet needs toclamp the sheets together.

A blind rivet is generally required to have high shear strength, and toexpand into any clearance between the rivet body and a hole in theworkpiece into which the rivet is inserted, in order to prevent thesheets of the workpiece from fretting under applied vibrations oroscillating applied loads. This is especially important in theautomotive industry.

It is also generally required that the rivets when set should have asingle roll-type bulged setting on the blind side of the workpiece,giving an increased tensile resistance to applied loading, whileproviding an aesthetic appearance.

In addition, it is generally desirable that the mandrel of the rivetbreak flush in the region of the rivet flange, contributing to anincrease in the shear resistance of the joint. In order to achieve theserequirements, especially in the case of higher strength blind rivets,the mandrel head is required to be fixed to the tail end of the rivetbody on assembly and to remain in place during and after setting, thuscontributing to the resistance to moisture ingress through the bore ofthe rivet body. In addition, by securing the mandrel head in the rivetbody, rattling of the mandrel head within the set rivet is avoided.

EP 0677666 discloses a blind rivet having a recess beneath the mandrelhead of the rivet. The tail end of the rivet body is crimped into anelliptically shaped recess beneath the mandrel head, and a furtherindentation is provided near to a flange portion of the rivet body.

GB 402813 shows a blind rivet having a mandrel head having a bevelledsurface beneath the head. This rivet suffers from the drawback that ithas a relatively narrow grip range.

GB 2231932 shows a blind rivet having a mandrel provided with groovesbeneath its head. On assembly of the rivet, the tail of the rivet bodyis swaged into the grooves to retain the mandrel in place duringmanufacture. As the mandrel stem is pulled to set the rivet, that partof the rivet body swaged to the mandrel beneath the mandrel head bulgesand begins to be forced outwards and out of engagement with the groovesin the mandrel stem. As the bulging process proceeds with setting, andthe mandrel continues to move through the rivet body, the mandrelgrooves then move into engagement with the internal bulge bore and themandrel is locked in place. However, this rivet suffers from thedrawback that there is often insufficient engagement of the mandrel tothe rivet body to prevent movement of the mandrel head relative to therivet body. In addition, when set in minimum grip thickness, this rivethas the disadvantage of providing a multi-fold rather than a singleroll-type setting.

U.S. Pat. No. 6,004,086 discloses a blind rivet in which the mandrel isprovided with grooves beneath the mandrel head. This rivet suffers fromthe drawback that if the rivet body is formed from stronger materialsuch as steel, the higher setting loads required to set the rivet causethe mandrel head to be pulled into the rivet body before setting iscomplete.

EP 1106845 discloses a blind rivet having a recess beneath the mandrelhead, into which the tail end of the rivet body is formed. This rivetsuffers from the drawback that the setting load for certain materialssuch as steel is high and as the maximum load is approached, the end ofthe rivet body deforms and the internal bore moves away from the recessformed below the mandrel head. This causes a gap to form between therecess and the rivet body, which enables the mandrel head to moverelative to the rivet body when the mandrel breaks.

GB 2416575 discloses a blind rivet in which a series of annular groovesare provided beneath the mandrel head. Although this type of rivetprovides an adequate grip range, the load required to set the rivet ishigh compared with other blind rivets, as a result of which the mandrelhead tends to loosen under recoil forces as the mandrel breaks atcompletion of setting of the rivet.

It can therefore be seen that all of the above rivets suffer from thedrawback that it is difficult to secure the mandrel head in the rivetbody to a sufficient extent during setting of the rivet. Preferredembodiments of the present invention seek to overcome one or more of theabove disadvantages of the prior art.

According to the present invention, there is provided a rivetcomprising:

a rivet body having a first shank adapted to be inserted into a hole ina workpiece and having an axial bore therethrough, and a flange at afirst end of the first shank for abutting the workpiece when the firstshank is inserted into the hole in the workpiece; and

a mandrel having a head, for engaging a second end of the first shank,and a second shank adapted to extend through the axial bore and to bepulled by a tool to set the rivet, wherein the head has an abutmentportion for abutting the first end of the first shank, and the secondshank has a first reduced diameter portion adapted to break when apredetermined tensile is loaded applied thereto during setting of therivet, and at least one protrusion adjacent said abutment portion fordefining a recess for receiving the first end of the first shank duringsetting of the rivet.

By providing at least one protrusion adjacent the abutment portion fordefining a recess for receiving the first end of the first shank duringsetting of the rivet, this provides the advantage of more securelyretaining the mandrel head in the rivet body during setting of therivet, which prevents movement of the mandrel head relative to the rivetbody and prevents subsequent rattling of the mandrel head in the rivetbody after setting of the rivet.

In a preferred embodiment, the rivet body is mounted to the mandrel andhas a second reduced diameter portion adjacent the first end of thefirst shank, and a third reduced diameter portion adjacent the secondend of the first shank.

This provides the advantage of providing a barrel shaped portion of therivet body, which assists bulging of the rivet body during setting ofthe rivet.

The rivet body may have an increased diameter portion between saidsecond and third reduced diameter portions, wherein, in a plane throughand parallel to the longitudinal axis of the rivet body, the anglebetween a line connecting the region of maximum external diameter withat least one of the regions of minimum external diameter and thelongitudinal axis of the rivet body is between 1.0 degree and 1.9degree.

The rivet may further comprise at least one first groove on said secondshank for receiving part of said second shank to define said thirdreduced diameter portion.

At least one said first groove may define a respective first surfaceinclined at a first acute angle relative to the longitudinal axis of thesecond shank.

At least one said first acute angle may be between 10 degrees and 20degrees relative to the longitudinal axis of the second shank.

The portions of reduced diameter of the rivet body may be arranged onopposite sides of the first reduced diameter portion when the rivet isassembled.

The first reduced diameter portion may be defined by a plurality ofindentations.

The abutment portion may comprise at least one second surface inclinedat a respective second acute angle to the longitudinal axis of thesecond shank.

At least one said second acute angle may be between 73 degrees and 78degrees relative to the longitudinal axis of the second shank.

The abutment portion may further comprise a lip arranged radiallyoutwards of the or each said first surface, wherein the lip defines arespective third surface adjacent each said second surface, and whereinthe or each said third surface is inclined at a respective third acuteangle, smaller than the corresponding said second acute angle, relativeto the longitudinal axis of the second shank.

At least one said protrusion may comprise a respective first rib.

The mandrel head may have at least one fourth surface inclined relativeto the longitudinal axis of the second shank for assisting insertion ofthe rivet into a hole in the workpiece.

A preferred embodiment of the invention will now be described, by way ofexample only and not in any limitative sense, with reference to theaccompanying drawings, in which:

FIG. 1 is a cross sectional elevation view of an assembled blind rivetembodying the present invention;

FIG. 2 is a side elevation view of a head of a mandrel of the rivet ofFIG. 1;

FIG. 3 is a cross sectional view from below of the mandrel head of FIG.2;

FIG. 4 is a cross sectional elevation view along the line A-A in FIG. 3;

FIG. 5 is a cross sectional elevation view along the line B-B in FIG. 3;and

FIG. 6 illustrates the rivet of FIG. 1 set at various thicknesses.

FIG. 1 shows a cross sectional elevation view of an assembled blindrivet 2 embodying the present invention. The rivet 2 has a rivet body 4mounted to a mandrel 6, the rivet body having a first shank 8 and anenlarged diameter flange portion 10 designed to abut a workpiece (notshown) when the first shank 8 is inserted into a hole in the workpiece.A barrel portion 12 formed by two smaller diameter portions 14, 16,extends from the flange portion 10, and a tail end 18 of the rivet body4 abuts the underside of a head 20 of the mandrel 6.

Referring to FIGS. 2 to 5, the mandrel head 20 has chamfered outersurfaces 22 to enable easy entry of the rivet 2 into a hole in theworkpiece, and a second shank 24 extends from the mandrel head 20 andhas a breakneck 26 formed by four indentations provided to enable thesecond shank 24 to break when a specific tensile load applied to themandrel 6 is exceeded.

Four inclined surfaces 28, each of which forms a tangent 25 to the shank24 of the mandrel 6, are provided underneath the mandrel head 20, thesurfaces 28 each being inclined at an angle of between 73 degrees and 78degrees, and preferably 75 degrees, relative to the longitudinal axis ofthe second shank 24. A lip 30 is also provided around the mandrel head20 to provide resistance to the tendency of the rivet body material tomove around the mandrel head 20 as the rivet is being set.

A series of grooves 32 are provided between the breakneck 26 and themandrel head 20, the grooves 32 defining a series of annular ribs 34,36. The uppermost rib 34 forms a cavity 38 between the mandrel head 20and the second shank 24, into which material of the rivet body 4 islocked and remains locked during and after the setting process. Thepresence of the uppermost rib 34 counteracts the tendency for themandrel head 20 to move inside the rivet body 4 as the mandrel 6 breaksor to move upwards relative to the rivet body 4 under recoil forcescaused by the breaking of the mandrel 6.

Other than the uppermost rib 34, each of the ribs 36 has an inclinedsurface 40 inclined at between 10 degrees and 20 degrees relative to thelongitudinal axis of the mandrel shank 24, but preferably 15 degrees.

In order to form the assembled rivet 2, the rivet body material isswaged into the grooves 32 in order to create the upper reduced diameterportion 16, the lower reduced diameter portion 14 is formed, and theformation of the reduced diameter portions 14, 16 causes a slight bow ofthe rivet body 4 to form the barrel portion 12 and induce a slight gap42 (FIG. 1) between the bore of the rivet body 4 and the shank 24 of themandrel 6. The angle of the bow of the outer surface of the rivet body 4(i.e. in a plane through and parallel to the longitudinal axis 46 of therivet body 4, the angle A₁ or A₂ between a respective line 48, 50connecting the region of maximum external diameter 52 with a respectiveone of the regions of minimum external diameter 54, 56 and thelongitudinal axis 46 of the rivet body 4) is between 1.0 degree and 1.9degree and is preferably 1.5 degree.

In order to set the rivet 2, the shank 24 of the mandrel 6 is pulled bymeans of a setting tool (not shown) while the flange 10 is supported bya nosepiece of the setting tool. As the shank 24 of the mandrel 6 ispulled, the rivet body 4 bulges, shortens in length to fill the hole inthe workpiece, and then collapses to give a blind side bulge 44, as bestseen in FIG. 6. Since the bulging or collapse of the rivet body 4 occursnearer to the end of the body than other types of rivet, the bulge issmall, but the bulge causes the body material to move away fromengagement with the grooves 32 in the mandrel shank 24. However, thebody material is retained in the recess 38 beneath the mandrel head 20to lock the mandrel 6 to the rivet body 4 so that the mandrel head 20and rivet body 4 are more securely attached to each other during andafter setting of the rivet. In this way, subsequent rattling of therivet is avoided, and the integrity and strength of the rivet joint isimproved.

It will be appreciated by persons skilled in the art that the aboveembodiment has been described by way of example only, and not in anylimitative sense, and that various alterations and modifications arepossible without departure from the scope of the invention as defined bythe appended claims.

The invention claimed is:
 1. A rivet for joining parts of a workpiecedefining a hole when the rivet is pulled by a tool to set the rivet byapplying a predetermined tensile load thereto, the rivet comprising: arivet body including a first shank defining an axial bore therethrough,the first shank having a first end and a second end, and a flange islocated at the first end of the first shank, the rivet body adapted tobe inserted into the hole in the workpiece such that the flange abutsthe workpiece when the first shank is inserted into the hole in theworkpiece; a mandrel including a head, with an abutment portion forabutting the second end of the first shank, and a second shank adaptedto extend through the axial bore and to be pulled by the tool, and thesecond shank has a first reduced diameter portion adapted to break atthe predetermined tensile load, and wherein the second shank furtherincludes at least one protrusion adjacent said abutment portion fordefining a recess for receiving the first end of the first shank duringsetting of the rivet; and wherein the at least one protrusion has aninclined surface at an angle greater than 20° from the longitudinal axisof the rivet.
 2. A rivet according to claim 1, wherein the rivet body ismounted to the mandrel and includes a second reduced diameter portionadjacent the first end of the first shank, and a third reduced diameterportion adjacent the second end of the first shank.
 3. A rivet accordingto claim 2, wherein the rivet body includes an increased diameterportion located between the second reduced diameter portion and thethird reduced diameter portion, and the increased diameter portionincludes a region of maximum external diameter, and the second reduceddiameter portion and the third reduced diameter portion each include aregion of minimum external diameter, and an imaginary line connectingthe region of maximum external diameter with at least one of the regionsof minimum external diameter forms with a longitudinal axis of the rivetbody an angle in the range of 1.0 degree to 1.9 degree.
 4. A rivetaccording to claim 3, wherein the second reduced diameter portion andthe third reduced diameter portion of the rivet body are arranged onopposite sides of the first reduced diameter portion of the mandrel. 5.A rivet according to claim 2, wherein the second shank further includesan annular rib, and the annular rib and the second shank define a firstgroove and the rivet body is compressed into the first grove to form thethird reduced diameter portion.
 6. A rivet according to claim 5, whereinthe annular rib includes a first surface inclined at a first acute anglerelative to a longitudinal axis of the second shank.
 7. A rivetaccording to claim 6, wherein the first acute angle is between 10degrees and 20 degrees.
 8. A rivet according to claim 1, wherein thefirst reduced diameter portion is formed by a plurality ofcircumferentially arranged indentations defined by the second shank. 9.A rivet according to claim 1, wherein the abutment portion includes asecond surface inclined at a second acute angle relative to alongitudinal axis of the second shank.
 10. A rivet according to claim 9,wherein the second acute angle is between 73 degrees and 78 degrees. 11.A rivet according to claim 9, wherein the abutment portion furthercomprises a lip arranged radially outwards of the second surface,wherein the lip defines a third surface adjacent the second surface, andwherein the third surface is inclined at a third acute angle, smallerthan the second acute angle, relative to the longitudinal axis of thesecond shank.
 12. A rivet according to claim 1, wherein the mandrel headincludes a chamfered surface inclined relative to a longitudinal axis ofthe second shank for assisting insertion of the rivet into the hole inthe workpiece.